(Proposal ID) S17A-164

(PI) Suzuki, Daisuke

(Proposal Title)
Extinction Law toward the Inner Milky Way

(Abstract)
We propose a deep imaging of the inner Galactic bulge of |l| < 3^{circ}, 
-2 < b < +0^{\circ}.5 by using Subaru/HSC with gr2i2zY filters to measure the 
spatial distribution of extinction ratio (i.e., A_{lambda}/A_{K_S}) that 
depends on wavelength as well. This measurement combined with the IRSF and/or 
VVV photometries allows us to build a new extinction model toward the inner 
Milky Way. The so called "standard" extinction law by Cardelli et al. 1989 is 
no longer applicable to the inner Galactic bulge with any total to selective 
extinction, R_V equiv A_V/E(B-V). The previous studies found that A_{V}/A_{K_S}
is 60-80 % higher than the standard extinction model in the bugle. To fully 
characterize the extinction ratio dependence on the wavelength, lambda, and 
(l, b), the multi-band, deep images for the wide bulge field are needed. Such 
an observation can be conducted only by Subaru/HSC. We perform the Red Clump 
method to robustly measure the extinction ratio in each filter. Our 
measurements will be applicable to wide range of observational astrophysics, 
such as, the dynamical and chemical evolution of the bulge, bulge structure, 
and 3D extinction map with standard candles (e.g., Cephieds, RR Lyraes) and 
parallax measurements by GAIA.